Such transmissions can comprise at least two shafts in addition to the input shaft, each of which is provided with a respective gear, the gears being connected by direction-controlling clutches with other gears which can be in mesh with one another and these gears, in turn, can be connected with yet other gears which ultimately mesh with a gear driving the output shaft (see U.S. Pat. No. 3,838,455).
In conventional transmissions for the aforedescribed purpose, the shafts which carry the transmission gearing, i.e. the gear and clutch shafts, are mounted in a transmission housing e.g. by being preassembled on the shaft outside the housing and then attached to the housing. For such purpose, the housing must be multipartite and must be provided with covers on the shaft bearings. A multipartite housing of this type is difficult and expensive to fabricate.
There is described in U.S. Pat. No. 3,465,609 a reversible transmission which uses clutches and provides, for the first and fourth speeds as well as for the output shaft, a separate housing apart from the housing which holds the transmission elements for the second and third speeds and for determining the direction of rotation of the output shaft. In this construction, like those discussed above, the bipartite configurations of the housing result in high construction costs.
When more than two speeds are required in a transmission of this type, moreover, it is necessary to provide an undesirably large axial dimension since, in this case, three shiftable clutches must be provided with the associated gear wheels on a common shaft.
Reference may be made to the German printed application (Auslegeschrift) DT-AS No. 1 920 985 which describes a reversible transmission having pairs or trains of gears which are continuously in mesh with one another and which use a one-piece transmission housing and which also has gear shafts fixed to the housing and upon which the transmission gears rotate. This housing is provided with a closable opening dimensioned to enable introduction of the transmission components and indeed premounted; assemblies of these elements (gears and clutches) could also be introduced through this opening. However, in this transmission it was necessary to use synchronous clutching arrangements and hence a synchromesh type construction which could not be accommodated readily to a load-switchable multispeed reversing transmission. The openings in the transmission serve merely to afford access and hence the construction was relatively complicated and, in many cases, caused problems with respect to the journaling of elements and interference between the window and, for example, the drive shaft or structures associated therewith. Furthermore, the transmission did not have an especially compact configuration.
Austrian Pat. No. OE-PS 271 123 describes a transmission without a ratio or speed change, e.g. a worm transmission which also uses a one-piece housing with especially large roller bearings whose diameters are greater than the largest diameters of the associated transmission parts. The bearing bores serving as the mounting openings are closed after mounting of the respective shafts by bearing covers. In this construction it is possible to use rotating drive shafts even with a one-piece housing but each shaft must then be provided with a mounting opening or bearing bore which is larger than the largest diameter of a part to be carried by the respective shaft. The provision of such a large number of relatively large openings is naturally inconvenient and structurally unsound and indeed may interfere with the rational positioning of the interacting parts.
A further transmission is described in British Pat. No. 704,445 in which premounted structural units are introduced into the transmission housing through mounting openings. This transmission, like those mentioned previously, must provide an opening for each of the premounted units which is sufficient to enable it to be introduced into the housing. This system, therefore, suffers from the same disadvantages of the earlier arrangements mentioned above.